Chronic obstructive pulmonary disease (COPD) includes conditions such as, e.g., chronic bronchitis and emphysema. COPD currently affects over 15 million people in the United States alone and is currently the third leading cause of death in the country. The primary cause of COPD is the inhalation of cigarette smoke, responsible for over 90% of COPD cases. The economic and social burden of the disease is substantial and is increasing.
Chronic bronchitis is characterized by chronic cough with sputum production. Due to airway inflammation, mucus hypersecretion, airway hyper-responsiveness, and eventual fibrosis of the airway walls, significant airflow and gas exchange limitations result.
Emphysema is characterized by the destruction or damage of the lung parenchyma. This destruction of the lung parenchyma leads to a loss of elastic recoil and tethering which maintains airway patency. Because bronchioles are not supported by cartilage like the larger airways, they have little intrinsic support and therefore are susceptible to collapse when destruction of tethering occurs, particularly during exhalation.
Acute exacerbations of COPD (AECOPD) often require emergency care and inpatient hospital care. An AECOPD is defined by a sudden worsening of symptoms (e.g., increase in or onset of cough, wheeze, and sputum changes) that typically last for several days, but can persist for weeks. An AECOPD is typically triggered by a bacterial infection, viral infection, or pollutants, which manifest quickly into airway inflammation, mucus hypersecretion, and bronchoconstriction, causing significant airway restriction.
Despite relatively efficacious drugs (e.g., long-acting muscarinic antagonists, long-acting beta agonists, corticosteroids, and antibiotics) that treat COPD symptoms, a particular segment of patients known as “frequent exacerbators” often visit the emergency room and hospital with exacerbations. These patients also have a more rapid decline in lung function, poorer quality of life, and a greater mortality risk.
Reversible obstructive pulmonary disease includes asthma and reversible aspects of COPD. Asthma is a disease in which bronchoconstriction, excessive mucus production, and inflammation and swelling of airways occur, causing widespread but variable airflow obstruction thereby making it difficult for the asthma sufferer to breathe. Asthma is further characterized by acute episodes of airway narrowing via contraction of hyper-responsive airway smooth muscle.
The reversible aspects of COPD include excessive mucus production and partial airway occlusion, airway narrowing secondary to smooth muscle contraction, and bronchial wall edema and inflation of the airways. Usually, there is a general increase in bulk (hypertrophy) of the large bronchi and chronic inflammatory changes in the small airways. Excessive amounts of mucus are found in the airways, and semisolid plugs of mucus may occlude some small bronchi. Also, the small airways are narrowed and show inflammatory changes.
In asthma, chronic inflammatory processes in the airway play a central role in increasing the resistance to airflow within the lungs. Many cells and cellular elements are involved in the inflammatory process including, but not limited to, mast cells, eosinophils, T lymphocytes, neutrophils, epithelial cells, and even airway smooth muscle itself. The reactions of these cells result in an associated increase in sensitivity and hyperresponsiveness of the airway smooth muscle cells lining the airways to particular stimuli.
The chronic nature of asthma can also lead to remodeling of the airway wall (e.g., structural changes such as airway wall thickening or chronic edema) that can further affect the function of the airway wall and influence airway hyper-responsiveness. Epithelial denudation exposes the underlying tissue to substances that would not normally otherwise contact the underlying tissue, further reinforcing the cycle of cellular damage and inflammatory response.
In susceptible individuals, asthma symptoms include recurrent episodes of shortness of breath (dyspnea), wheezing, chest tightness, and cough. Currently, asthma is managed by a combination of stimulus avoidance and pharmacology.
Bronchiectasis is a condition where lung airways become enlarged, flabby, and/or scarred. In the injured areas, mucus often builds up, causing obstruction and/or infections. A cycle of repeated infections may continue to damage the airways and cause greater mucus build-up. Bronchiectasis can lead to health problems such as respiratory failure, atelectasis, and heart failure.
Strategies for managing COPD and other conditions of the lung include smoking cessation, vaccination, rehabilitation, and drug treatments (e.g., inhalers or oral medication). Drug treatments of COPD conditions, such as, e.g., mucus production, inflammation, and bronchoconstriction often suffer from poor patient compliance. That is, certain patients may not accurately administer prescribed doses, reducing the efficacy of treatment. For drug treatments utilizing inhalation, there is also an accompanying drug loss due to upper airway entrapment, which may lead to an over-prescription of active drugs. Also, inhalation treatments can be ineffective at treating smaller airways of the lung (e.g., airways that are smaller than 2 mm). For drug treatments utilizing oral administration, there is an accompanying systemic loss which also leads to an over-prescription of active drugs. The over-prescription of drugs may result in suboptimal treatment and/or a build-up of toxins within the lungs and/or other organ systems. In other situations, drugs may not be deposited evenly to areas of the lungs because of particle size and/or blockage of airways preventing the drugs from reaching distal regions of the lungs (e.g., a heterogeneous delivery of drugs). Blockages may be caused by mucus and narrowing of the airway due to inflammation and remodelling.
The use of radiofrequency (RF) energy in medical applications is rapidly increasing. RF energy can be used to treat a variety of conditions affecting numerous body systems, such as, e.g., the respiratory system, the circulatory system, the digestive system, the immune system, the muscular system, among others. Various non-drug energy delivery procedures for, among other things, treatment of COPD, such as, e.g., severe persistent asthma, for which inhaled corticosteroids and long-acting beta-agonists are an insufficient treatment. In order to apply the energy delivery procedures, a catheter may be positioned to deliver thermal energy to a body lumen, such as a lung airway wall, for reducing excessive airway smooth muscle (ASM), and clear the air pathway within the trachea or lungs of a patient. The catheter may include an electrode array at a distal portion, which may be manually expanded to position the electrode array in communication with the airway wall. The electrode array may be coupled to one or more thermocouple wires for determining temperature of the electrode array to control the thermal energy delivered to the airway wall.
Conventionally, the electrode array can include elongated electrodes, which are welded together and coupled to hypotubes at their distal and proximal ends. Since the electrode array and the hypotubes are conductive to each other, welding of the electrode array only allows for monopolar design of delivering electrical energy to the electrode array. Moreover, in conventional arrangements, less space is available for the thermocouple wire to extend proximally through a proximal hypotube attached to the electrode array due to welding of the electrode array.
Therefore, there exists a need for an improved catheter design that permits different configurations (including, e.g., monopolar or bipolar configurations) for the delivery of electrical energy to body lumens, and increases effective space available for, among other things, thermocouple wire attachment. The improved catheter designs would also reduce the number of steps needed to assemble and/or manufacture the electrode array by, e.g., eliminating the need for welding together multiple electrodes of the electrode array. In other examples, there exists a need for other improvements. For example, certain electrode arrays, e.g., monopolar electrode arrays, may create uneven heating distribution, and may concentrate heating in the regions surrounding the electrodes to undesirable levels.